When using Arturia's Keylab 88 with Bitwig (2.2.3 on Linux) I encounter random loud notes while playing, regardless of how the key was actully played. This seems to happen mostly when the state of the sustain pedal changes (pressed / released). Manipulation of the Keylab's faders or knobs while playing may trigger this, too.

Over on the Arturia forums it was suggested that this happens when a (sysex) event is sent to update the Keylab's display, so it might be related to the keyboard's firmware (when pressing / relasing the pedal a display update happens).

Outside of Bitwig this does not seem to happen, e.g., using the Keylab directly with Pianoteq works just fine.

I've just noted that disabling the midi-out in the controller settings for the Keylab makes the loud nodes go away. So it seems quite reasonable this issue has something to do with Bitwig sending something to the controller, possibly those sysex events mentioned above.
I am wondering what Bitwig is trying to send to the display, as there is just some kind of flicker when the sustain pedal's state changes (if midi-out is disabled, the Keylab shows the current value of the pedal).

As an aside: this issue happens on Linux and Windows, and independent of the VST plugin used.

Not an answer as such, but may help you get to the bottom of things - I had a similar issue with a different MIDI device and used a tiny free/donationware application called MIDI-OX and it was really useful at helping to spot spurious MIDI events being fired and which ones they were. I got around my issue (I was using Reaper at the time) by building a JS script that filtered out the spurious MIDI events, but no idea what the equivalent would be in Bitwig Studio or if it's even possible.